113 lines
2.9 KiB
Java
113 lines
2.9 KiB
Java
/*
|
|
* Name: Mike Cifelli
|
|
* Course: CIS 443 - Programming Languages
|
|
* Assignment: Lisp Interpreter 2
|
|
*/
|
|
|
|
package eval;
|
|
|
|
import parser.*;
|
|
|
|
/**
|
|
* <code>SETF</code> represents the SETF form in Lisp.
|
|
*/
|
|
public class SETF extends LispFunction {
|
|
|
|
private static SymbolTable environment = new SymbolTable();
|
|
|
|
/**
|
|
* Look up the value of a symbol using its name.
|
|
*
|
|
* @param symbolName
|
|
* the name of the symbol to look up
|
|
* @return
|
|
* the value of <code>symbolName</code> if it has one; null otherwise
|
|
*/
|
|
public static SExpression lookup(String symbolName) {
|
|
SymbolTable current = environment;
|
|
|
|
while (current != null) {
|
|
if (current.contains(symbolName)) {
|
|
return current.get(symbolName);
|
|
}
|
|
|
|
current = current.getParent();
|
|
}
|
|
|
|
return null;
|
|
}
|
|
|
|
/**
|
|
* Set the current environment to the specified value.
|
|
*
|
|
* @param newEnvironment
|
|
* the value to set the environment to
|
|
*/
|
|
public static void setEnvironment(SymbolTable newEnvironment) {
|
|
environment = newEnvironment;
|
|
}
|
|
|
|
/**
|
|
* Retrieve the current environment.
|
|
*
|
|
* @return
|
|
* the current environment
|
|
*/
|
|
public static SymbolTable getEnvironment() {
|
|
return environment;
|
|
}
|
|
|
|
// The number of arguments that SETF takes.
|
|
private static final int NUM_ARGS = 2;
|
|
|
|
public SExpression call(Cons argList) {
|
|
// retrieve the number of arguments passed to SETF
|
|
int argListLength = LENGTH.getLength(argList);
|
|
|
|
// make sure we have received the proper number of arguments
|
|
if (argListLength != NUM_ARGS) {
|
|
Cons originalSExpr = new Cons(new Symbol("SETF"), argList);
|
|
String errMsg = "too " +
|
|
((argListLength > NUM_ARGS) ? "many" : "few") +
|
|
" arguments given to SETF: " + originalSExpr;
|
|
|
|
throw new RuntimeException(errMsg);
|
|
}
|
|
|
|
SExpression symbol = argList.getCar();
|
|
|
|
// make sure the first argument is a symbol
|
|
if (! symbol.symbolp()) {
|
|
throw new RuntimeException("SETF: " + symbol + " is not a symbol");
|
|
}
|
|
|
|
Cons cdr = (Cons) argList.getCdr();
|
|
SExpression value = EVAL.eval(cdr.getCar());
|
|
|
|
SymbolTable current = environment;
|
|
|
|
// set 'current' to the symbol table that contains 'symbol' or the
|
|
// global symbol table if 'symbol' is not in the environment
|
|
while ((! current.contains(symbol.toString())) &&
|
|
(current.getParent() != null)) {
|
|
current = current.getParent();
|
|
}
|
|
|
|
current.put(symbol.toString(), value);
|
|
|
|
return value;
|
|
}
|
|
|
|
/**
|
|
* Determine if the arguments passed to this Lisp function should be
|
|
* evaluated.
|
|
*
|
|
* @return
|
|
* <code>false</code>
|
|
*/
|
|
public boolean evaluateArguments() {
|
|
return false;
|
|
}
|
|
|
|
}
|